Methods of preparing moldings by compressing and solidifying molding material, representative of which is powdery/granular material, are generally used in a wide range of industry including, for example, not only industrial fields of pharmaceuticals and foods (functional foods and general foods) but also fields of electronic materials such as molding of semiconductor encapsulating resin, battery-related products, powder metallurgy-related products, electronic functional parts and the like, and fields of agricultural chemicals and sanitary products. Among those, in the field of pharmaceuticals, the molding incorporating a core therein is called “a dry coated tablet” since such a molding is prepared by compression-molding molding material to form an outer layer around a core (core tablet).
Conventionally, a molding with core such as a dry coated tablet, is prepared by a method including: previously preparing a core as a molding by means of a separate tablet machine; feeding the core as the molding into a die of a dry coated tablet machine fed and filled with molding material for outer layer; further feeding the molding material for outer layer; and compression-molding the core and molding material for outer layer. This manufacturing method involves serious problems of a larger amount of operation and a lower production efficiency than a method of preparing an ordinary compressed molding. Further, the method of concern involves problems associated with feeding of cores, such as an occurrence of a tablet with no core or multiple cores, displacement of a core in a tablet, and the like and hence requires a complicated mechanism or apparatus for monitoring the feeding of cores and checking final molded products to assure the quality of each molding, thus resulting in the machine increased in size and complicated in structure.
In view of such circumstances, the inventors of the present invention invented a method and apparatus for efficiently preparing a molding with core from such molding material as powdery/granular material at a time, as described in patent document 1. This manufacturing method uses compression molding means having a die and upper and lower punches, at least the upper punch of which, preferably both of which have a double structure comprising a center punch and an outer punch surrounding the outer periphery of the center punch, both of which are slidable and capable of compressing operation. This manufacturing method basically uses double-structured upper and lower punches and includes the steps of feeding and filling respective of molding material for core and molding material for outer layer, the step of compression-molding the molding material for core and/or the molding material for outer layer, and the step of compression-molding the whole molding containing a core. This patent document 1 describes a rotary compression molding machine of the type configured to cause the center punch and the outer punch to perform their respective compressing operations independently for practicing this method. Such a compression molding machine has a complicated compression mechanism. The same holds true for patent document 2 disclosing a compression molding machine configured to prepare the molding of the type different from the type with core.
Further, the inventors of the present invention invented a rotary compression molding machine described in patent document 3 as an apparatus for practicing the aforementioned method of preparing a molding with core. The compression molding machine described in patent document 3 includes a double-structured upper punch having a center punch capable of protruding its head from the head of the outer punch. In a condition where the head of the center punch is most protruded from the head of the outer punch, the center punch and the outer punch come into engagement with each other with their respective punch tips substantially aligned with each other so as to be capable of operating as one piece. Though this type of double-structured upper punch is capable of assuming a position in which the center punch tip and the outer punch tip are substantially aligned with each other and a position in which the center punch tip is protruded from the outer punch tip, this double-structured upper punch is structurally incapable of assuming a position in which the outer punch tip is protruded from the center punch tip.
On the other hand, a double-structured lower punch has a structure in which the center punch head portion is protruded from the outer punch end portion. In a condition where the center punch is most deeply inserted into the outer punch on the opposite side away from the punch tip; stated otherwise, the center punch is most deeply thrust into the outer punch toward the center punch tip side, the center punch and the outer punch come into engagement with each other with their respective punch tips substantially aligned with each other so as to be capable of operating as one piece. Though this type of double-structured lower punch is capable of assuming a position in which the center punch tip and the outer punch tip are substantially aligned with each other and a position in which the outer punch tip is protruded from the center punch tip, this double-structured lower punch is structurally incapable of assuming a position in which the center punch tip is protruded from the outer punch tip. Since the double-structured punch described in patent document 3 is thus configured to operate with its center and outer punches engaged with each other, the rotary compression molding machine has limitation on its punch movements, though its compression mechanism is simplified.
Other double-structured punches include a double-structured punch of the type having a center punch fixed. This type of double-structured punch is used to prepare a molding having a hollow extending through a central portion thereof, for example, a troche used as a medicine or a food and the like. In the case of the double-structured punch having a center punch fixed, a lower punch has a double-structure of a center punch and an outer punch, and an upper punch has a central hollow for receiving the lower center punch in it during compressing. The lower center punch and the hollow of the upper center punch make it possible to prepare a molding having a central hollow. This is the example of the double-structured punch having a center punch fixed, on the other hand, double-structured punches of the type having a freely slidable center punch include, in addition to the double-structured punch described in the aforementioned patent document 1, a double-structured punch of the type having a movable center punch for molding of ceramic, ferrite or the like (non-patent document 1). This double-structured punch is configured such that its center punch and outer punch slide as independently guided by their respective punch rails formed in the compression molding machine. During compression, the center punch and the outer punch are independently pressed by respective compressing sections subjected to pressing operation of the compression molding machine. For this reason, such a double-structured punch is usually not structured to bring the center punch and the outer punch into engagement with each other for compression as in the case of the double-structured punch described in the patent document 3.    Patent Document 1: International Laid-Open Publication No. WO 01/98067 pamphlet    Patent Document 2: International Laid-Open Publication No. WO 03/018302 pamphlet    Patent Document 3: International Laid-Open Publication No. WO 02/090098 pamphlet    Non-patent Document 3: “PROBLEM ASSOCIATED WITH SHAPING BY CERAMIC POWDER MOLDING AND REMEDY THEREFOR —CHARACTERISTICS OF AND PROBLEMS WITH POWDER CNC MULTIPLATEN PRESS”, Journal of Society of Powder Technology, Japan, p184-194 (2001)